i saw on another forum people using the firestick 4k and enabling some developer options it'll display video source information and that should display hdr10+ if you tv is capable of

It won't tell you if your TV supports HDR10+. The person who posted that owns an LG TV which doesn't support HDR10+. The video source information is displayed regardless of which TV you have. It only shows you the highest form of HDR supported by the content.